The present invention pertains to the art of adjustable-length telescoping tubes and more particularly to the locking mechanism therein.
The invention is particularly applicable to the adjustable-length canes, crutches, walkers, and the like and will be described with particular reference thereto. However, it will be appreciated that the invention has broader applications such as adjustable height chairs and commodes and may be advantageously employed in other environments and applications.
Adjustable-length tubes are typically composed of at least two telescoping, hollow, sleeves or tubes. The basic assembly comprises a first or inner tube slidably inserted in a second or outer tube. The inner tube has a sidewall opening while the outer tube has a series of openings spaced lengthwise along its sidewall. A spring-loaded button, or snap button as it is commonly referred to, is positioned in the interior of the inner tube. The button is dimensioned to protrude through the sidewall opening in the inner tube and outwardly through one of the openings in the outer tube.
A spring element, typically a U-shaped wire, is secured to the back of the button. One prong of the wire is attached to the button and the other prong extends to the opposite side of the inner tube sidewall. The wire urges the button through the opening in the inner tube sidewall. Since the button also protrudes through one of the openings in the outer tube sidewall, the tubes are locked relative to one another, thus locking the length of the telescoping tube assembly. U.S. Pat. Nos. 4,044,784; 4,528,998; and 5,139,040 generally show and describe this type of snap button assembly.
To adjust the length of the assembly, the spring-loaded button is pushed against the biasing force of the spring element through the outer tube opening toward the inner tube. Once the snap button clears the interior surface of the outer tube, the tubes are free to slide lengthwise relative to one another. The outer tube is then moved to a desired position relative to the inner tube, and the button aligned with a selected opening in the outer tube to achieve the desired axial length of the tube assembly.
One problem with prior art arrangements is that the snap button could be inadvertently moved from its registration with the opening in the inner tube if excessive force is imposed on the snap button. The outer surface of the button can potentially pass beneath the sidewall of the inner tube, allowing the snap button to become dislodged therein. Returning the button to the inner tube opening, unfortunately, requires disassembly to access and reposition the spring button in the inner tube.
Some adjustable-length tube assemblies have devices which decrease the play and rattle between the tubes of the assembly. For example, U.S. Pat. No. 4,085,763 addresses this problem in a cane by employing an annular stabilizing collar. The collar is slidably received over the inner tube and held in place with a wing-type male set screw. By tightening down the set screw, the outer tube is stabilized relative to the inner tube.
In U.S. Pat. No. 4,044,784, a swivel lock is used to fix an outer tube with respect to an inner tube. The swivel lock includes a sleeve in threaded engagement with an externally threaded portion on one end of the outer tube. The sleeve fits closely about the exterior surface of the inner tube to limit movement of the outer tube.
U.S. Pat. Nos. 4,596,484 and 4,029,279 show stabilizing arrangements using a lever type device. However, the locking mechanisms of these devices add additional weight, are fairly complex and difficult to use.
In the above patents, the anti-rattle mechanism is separate from the snap button. This requires additional manufacturing and assembly steps which add significantly to the cost thereof.
Therefore, it has been deemed desirable to develop an integral snap button and anti-rattle member for use in adjustable tube assemblies. The member provides easy adjustment of the length of the tubes, a high degree of stability, and is simple and economical to manufacture.